JP4462605B2 - Aqueous silica dispersion - Google Patents

Description

  The present invention relates to an aqueous silica dispersion used for coating various substrate surfaces by coating, impregnation and the like.

  Conventionally, synthetic resin emulsion-based coating materials have been used to prevent deterioration of inorganic base materials such as concrete and ceramic building materials, organic base materials, metal materials and the like. Immediately after application, the coating material forms a strong coating film by physical adhesion. However, generally no chemical bond is formed between the coating film and the substrate surface, and the synthetic resin is hydrophobic, so it has a particularly good affinity with highly hydrophilic inorganic substrates and metal surfaces. Is low and it is difficult to maintain a good coating state for a long time. Furthermore, since the synthetic resin itself deteriorates due to heat, ultraviolet rays, etc., there is a big problem in the durability of the coating film. In addition, it decomposes by fire and generates harmful gases. Even if it is discarded, it is not preferable as it is not adapted to the environment.

  On the other hand, silica is a material that is more suitable in terms of environment and resources because it has higher hydrophilicity than non-synthetic resins, is nonflammable, and is a metal oxide located at the first position of the crust constituent metal oxide.

  So far, dispersions and coating materials mainly composed of silica have been proposed. For example, a silica sol solution, a water glass solution, and a mixed solution thereof have been proposed (see, for example, Patent Documents 1 and 2).

However, the dispersions and the like disclosed in the above documents are desired to be improved in terms of low stability, such as gel formation in the liquid, and low durability of the formed coating film. It was.
JP-A-10-158585 JP 2000-109722 A

  An object of the present invention is to provide an aqueous silica dispersion excellent in coating property and durability of a formed coating film, which can be used as a coating material or an impregnating material for coating of various substrate surfaces. To do.

  An aqueous silica dispersion having a specific solid content silica content is excellent in coating properties and durability of the formed coating film, and is suitable as a coating material or impregnating material for coating of various substrate surfaces. I found out. It was also found that the coating structure and durability are affected by the chemical structure of the silica component and the average particle size of the water-dispersed particles. Based on this finding, the present invention has been completed.

That is, the present invention
[1] An aqueous silica dispersion having a solid content of 5 to 75% by weight and a silica component content of 97 to 99% by weight in the solid content,
[2] A coating film formed using the aqueous silica dispersion according to [1],
And [3] an inorganic porous body water absorption inhibitor comprising the aqueous silica dispersion according to [1],
About.

  The silica dispersion of the present invention has excellent coating properties and durability of the formed coating film, and can be used as a coating material or an impregnation material for coating on various substrate surfaces. Moreover, since the obtained coating film has water absorption inhibitory capacity, this silica dispersion liquid can function as an inorganic porous body water absorption inhibitor.

  The aqueous silica dispersion of the present invention (hereinafter referred to as silica dispersion) has a solid content of 5 to 75% by weight, and the silica component content in the solid content is 97 to 99% by weight. Is one major feature. Because of having such a configuration, coating properties on various substrate surfaces such as inorganic substrates, organic substrates, metal materials, and durability of coating films formed on the surfaces (hereinafter simply referred to as durability) Excellent). From the viewpoint of expression of the desired effect of the present invention, the solid content is preferably 5 to 60% by weight, more preferably 10 to 45% by weight. The content of the silica component in the solid content is preferably 97.5 to 98.5% by weight. Here, the content (% by weight) of the solid content is 50 in a dryer (ADVANTEC, model number: FC-410) after putting the silica dispersion in a glass petri dish (flat petri dish, product number: 70, diameter 75 mm). The weight of the dried product obtained by drying at 0 ° C. for one day is measured, and the weight of the dried product is determined by dividing by the weight of the silica dispersion previously measured and multiplying by 100.

  The silica dispersion of the present invention comprises a sol in which solid particles are uniformly dispersed in an aqueous medium. Here, the dispersion refers to a state in which no gel-like material derived from aggregation of solid particles is present in the medium, and whether or not it is in a dispersed state can be determined by the presence or absence of the gel-like material by visual observation. More specifically, it is possible to determine that the dispersion is in a dispersed state by subjecting the silica dispersion to a 1 mm mesh sieve and visually confirming that the entire amount of the dispersion passes through the sieve. . In the silica dispersion of the present invention, the solid particles are uniformly dispersed without forming a gel, so the coating properties are excellent, and therefore the film thickness and film density during film formation can be made uniform. This contributes to improving the durability of the coated film.

  Examples of the aqueous medium include water alone or a mixture of water and an aqueous organic material such as alcohol, surfactant, and siliconate described below. The amount of water in the mixture is preferably 25 to 95% by weight.

  The solid content is mainly composed of an insoluble silica component. The silica component as used in the field of this invention means the compound which contains Si. In the present specification, the silica component also includes an alkali silicate used when preparing the silica dispersion. Examples of solids other than the silica component include alkali metal oxides, alkali metal salts, alkaline earth metal oxides, alkaline earth metal salts, and groups 3B, 4B, and 5B such as phosphorus, boron, aluminum, and germanium. And at least one selected from the group consisting of oxides and salts of group elements. More specifically, the solid content is at least one selected from the group consisting of alkali metal oxides, alkali metal salts, alkaline earth metal oxides, alkaline earth metal salts, phosphorus oxides, and boron oxides. Is preferred. These solid components other than the silica component contribute to the formation of the network structure by the silica component in the coating film formation process and the modification of the network structure.

The silica component contained in the silica dispersion of the present invention desirably has a specific chemical structure from the viewpoint of improving the coating properties and durability of the silica dispersion. Specifically, when ²⁹ Si-NMR measurement is performed on a dried silica dispersion (for example, a medium removed by maintaining at 25 ° C. for 72 hours), the attribution of the spectrum by ²⁹ Si-NMR of the silica component The ratio of the area of the signal showing the Q ₂ structure to the total area of the signal showing the Q _n (n = 0-4) structure (hereinafter referred to as the relative amount of the Q ₂ structure) is preferably 5% or less, more preferably The ratio of the area of the signal showing the Q ₃ structure to the area of the signal showing the Q ₄ structure (hereinafter referred to as Q ₃ / Q ₄ ratio) is preferably 0.1 ≦ Q ₃ / Q ₄ ≦ It is desirable to have a chemical structure of 0.6, more preferably 0.1 ≦ Q ₃ / Q ₄ ≦ 0.5.

Here, the Q _n structure is a chemical structure determined according to the number of bridging oxygen atoms (oxygen atoms bonded to two Si atoms) among the oxygen atoms of the SiO ₄ tetrahedron unit that is a structural unit of silica. Q _n is the degree of bonding of SiO ₄ units, and n is the number of bridging oxygen atoms. It is known that the chemical shift of a signal indicating such a structure by ²⁹ Si-NMR measurement varies depending on the degree of bonding Q _n . The chemical shift (TMS standard) of the signal indicating the Q _n structure varies according to the liquid and solid, compound type, but is generally assigned as follows ["Glass Science Fundamentals and Applications" by Sakuo Sakuo, published Company: Uchida Otsukuru, 1997].

Structure chemical shift
Q ₀ : −65 to −75 ppm
Q ₁ : −76 to −84 ppm
Q ₂ : −85 to −90 ppm
Q ₃ : −92 to −100 ppm
Q ₄ : −105 to −115 ppm

In order to obtain good film formability, it is necessary for SiO ₂ to form an appropriate network structure. The structures of Q ₀ , Q ₁ , and Q ₂ are point or linear bonds and do not form a network structure. It also tends to dissolve in water. The Q ₃ and Q ₄ structures form a network structure, but the Q ₄ structure alone tends to be rigid, and the balance between the Q ₃ structure and the Q ₄ structure is important in terms of coating properties. In this respect, the Q ₃ / Q ₄ ratio is preferably in the range of 0.1 to 0.6.

That is, from the viewpoint of improving durability (for example, water resistance, weather resistance, etc.) by forming a network structure with a silica component, it is preferable that the Q ₀ , Q _1, and Q ₂ structures are small. Q _0, among the Q ₁ and Q _2, since the presence of Q ₀ and Q ₁ is not more than half Q ₂ 'each, to represent the relative amounts of these are representative Q ₂ structure, the relative Q _2' Structure The amount is preferably 5% or less. Further, from the viewpoint of improving the coating property by forming a long-distance network structure between silica components, it is preferable that the Q ₄ structure does not exist in an excessive ratio. In the present invention, from the viewpoint of improving both the coating properties and durability of the silica dispersion, the optimum conditions for the existence ratio of individual Q _n structures were found. As a result, the chemical structure of the silica component can be optimized, and a silica dispersion having excellent coating properties and durability can be provided.

  Further, the average particle size of the solid particles dispersed in the silica dispersion of the present invention (the solid particles are substantially composed of a silica component) is determined by both the coating properties and durability of the silica dispersion. From the viewpoint of improvement, it is preferably in the range of 0.01 to 0.8 μm, more preferably in the range of 0.05 to 0.5 μm, and further in the range of 0.05 to 0.2 μm. preferable. The average particle size of the solid content particles is usually 0.01 μm or more, preferably 0.05 μm or more from the viewpoint of improving the durability of the coating film by forming a silica component network structure, and improving the uniformity of the coating film. In view of the above, 0.8 μm or less is preferable. The average particle size of the solid particles is, for example, a laser diffraction particle size distribution measuring device (LA-920 manufactured by Horiba, Ltd.), circulation speed 4, ultrasonic intensity 7, ultrasonic time 1 minute, relative refractive index. It can be obtained by measuring the silica dispersion under the condition 1.1.

  Further, from the viewpoint of further improving the durability of the silica dispersion of the present invention, it is preferable that the silica component has a property capable of imparting water repellency to the formed coating film. The method for imparting such properties is not particularly limited, but it is preferable from the viewpoint of simplicity and effectiveness to introduce Si that forms Si—C bonds into the silica component.

  Since the silica dispersion of the present invention is excellent in durability, the silica component may not necessarily contain Si that forms Si—C bonds, but it is applied with water repellency applied to the coating film. From the viewpoint of further improving the durability of the film, the silica component includes a silica component containing Si that forms a Si—C bond as a structural unit, and a silica component that does not contain Si that forms a Si—C bond as a structural unit. Or a silica component containing Si as a structural unit forming a Si—C bond.

  Specifically, for example, in the silica dispersion of the present invention, from the viewpoint of imparting water repellency to the formed coating film, a hydrophilic group and an alkyl group imparting appropriate hydrophobicity are combined in the silica component. A compound having a compound (compound having a Si—C bond) may be included. Further, the silica dispersion of the present invention may be prepared by mixing the silica sol used in the silica dispersion and the compound and then performing a condensation reaction.

  Examples of the compound having a Si—C bond include alkyl siliconates and alkyl silanes.

For example, as the alkyl siliconate, it is preferable to use a compound represented by the following general formula.
_{R n -Si- (OM) 4-} n
In the formula, n represents the number of bonds of R with Si, and is 1, 2 or 3. R represents an alkyl group, and the alkyl group preferably has 1 to 2 carbon atoms. M represents either a hydrogen atom or an alkali metal atom. Specific examples of the compound include sodium methyl siliconate [CH ₃ Si (OH) ₂ (ONa)] and potassium ethyl siliconate [C ₂ H ₅ Si (OH) ₂ (OK)].

Further, as the alkylsilane, it is preferable to use a compound represented by the following general formula.
R ¹ —Si (OR ² ) ₃
In the formula, R ¹ and R ² represent the same or different alkyl groups, and R ¹ preferably has 1 to 3 carbon atoms, and R ² has preferably 1 to ² carbon atoms. Specific examples of the compound include methyltrimethoxysilane, ethyltrimethoxysilane, hexyltrimethoxysilane, decyltrimethoxysilane, methyltriethoxysilane, propyltriethoxysilane, hexyltriethoxysilane, decyltriethoxysilane, and the like. Is mentioned.

  Introduction of Si that forms Si—C bonds into the silica component can be carried out, for example, by adding an alkylsiliconate at the time of preparing the silica dispersion or after the preparation and mixing them uniformly. The addition amount of the alkyl siliconate is preferably 0.1 to 20 parts by weight, more preferably 1 to 20 parts by weight with respect to 100 parts by weight of the silica component in the silica dispersion at the time of preparation before addition of the alkyl siliconate or after preparation. 10 parts by weight. Also, for example, a condensation reaction product obtained by subjecting alkylsilane to a condensation reaction using an acid (for example, 0.005N hydrochloric acid solution) or an alkali (for example, 0.02 (v / v)% aqueous ammonia) as a catalyst. Can be carried out by mixing uniformly during or after the preparation of the silica dispersion. The addition amount of the condensation reaction product is preferably 0.1 to 20 parts by weight, more preferably 1 to 20 parts by weight with respect to 100 parts by weight of the silica component in the silica dispersion during preparation before or after the addition of the condensation reaction product. 10 parts by weight. Further, for example, the condensation reaction product can be mixed with a commercially available water glass and then subjected to dealkalization treatment. The addition amount of the condensation reaction product is preferably 0.1 to 20 parts by weight, more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the silica component in the water glass. In the silica dispersion containing Si that forms Si—C bonds obtained in this way, the dry film exhibits water repellency, and the durability of the coating film is further improved.

  When the silica dispersion contains Si that forms a Si—C bond, the content of Si that forms a Si—C bond is preferably 0.01 to the total Si contained in the silica dispersion. 30 mol%, More preferably, it is 0.01-10 mol%, More preferably, it is 0.1-5 mol%.

  In such a case, the content of Si that forms Si—C bonds in the total Si can be measured, for example, by the following method.

That is, the silica dispersion is maintained at 25 ° C. for 72 hours, and the dried product from which the medium has been removed is subjected to ²⁹ Si-NMR measurement. Here, in the assignment of the spectrum by ²⁹ Si-NMR, the chemical shift of Si (R—SiO ₃ ; R represents an alkyl group) forming a Si—C bond is in the range of −40 to −70 ppm. The chemical shift of Si (SiO ₄ ) that forms only O bonds is in the range of −65 to −115 ppm, and both peaks can be separated and assigned [Encyclopedia of nuclear magnetic resonance, Vol. 7, pp4386-4398. John Wiley & Sons Ltd. (1996)]. Therefore, the ratio (P) of the area of signals attributed to Si that forms Si—C bonds in the total area of signals attributed to both Si (area of signals attributed to all Si) is expressed as follows. formula:

Ask for. The value of P corresponds to the value of the ratio (mol%) of Si that forms Si—C bonds in the total Si when the total Si is 100 mol%. The content (mol%) of Si that forms Si—C bonds is obtained.

  In addition, when the silica dispersion liquid of this invention contains Si which forms a Si-C bond, as solid content in a silica dispersion liquid, Preferably it is 5 to 30 weight%.

  As the silica dispersion of the present invention, those containing a surfactant and / or alcohol are preferable from the viewpoint of improving the permeability to the substrate.

  As the surfactant, any of a cationic surfactant, an anionic surfactant, an amphoteric surfactant, and a nonionic surfactant may be used. As the cationic surfactant, for example, linear alkylbenzene sulfonate, polyoxyethylene addition alcohol sulfate, and alkyl sulfate are preferable, and as the anionic surfactant, for example, alkyl ether sulfate sodium salt, alkyl sulfate. Trimethylammonium salts and alkylpyridinium salts are preferable. Examples of amphoteric surfactants include alkylcarboxybetaines and alkylsulfobetaines. Examples of nonionic surfactants include polyoxyethylene alkyl ethers and polyoxyethylenes. Alkyl phenyl ether and fatty acid diethanolamide are preferred. In addition, as said alkyl, a C6-C22 thing is preferable and a C8-C14 thing is more preferable.

  Any alcohol can be used as long as it is hydrophilic, and examples thereof include methanol, ethanol, normal propanol, and isopropanol.

  The content of the surfactant and / or alcohol in the silica dispersion is preferably 0.01 to 10% by weight, more preferably 0.1 to 1% by weight.

  Further, the ceramic dispersion of the present invention may contain various ceramic powders and / or color pigments depending on the application and desired function.

  The type of ceramic powder is not particularly limited. For example, alumina, magnesia, zirconia, titania, iron oxide, zinc oxide, silica, mica, talc and other oxides, spinel, perovskite and other double oxides, carbonized Non-oxide powders such as silicon, titanium carbide, boron carbide, boron nitride, silicon nitride, and aluminum nitride are listed, and at least one of them is preferably used. Although the kind of coloring pigment is not specifically limited, use of an inorganic pigment, an organic pigment, a phosphorescent pigment, etc. is suitable.

  The average particle diameter of the ceramic powder and the color pigment is preferably 0.01 to 100 μm from the viewpoint of dispersibility. The average particle diameter can be measured in the same manner as in the case of the solid particles.

  The content of the ceramic powder and / or the color pigment in the silica dispersion is preferably 0.01 to 10% by weight, more preferably 0.1 to 5% by weight.

  In the silica dispersion of the present invention, after preparing the silica sol, the sol is appropriately mixed so that the solid content and the silica component content in the solid content are in a predetermined ratio, and other components are optionally added. It can be prepared by adding and mixing. The silica dispersion of the present invention is preferably prepared, for example, by obtaining a silica sol and then adding and mixing an alkali silicate aqueous solution or an alkali metal salt aqueous solution to the sol. Examples of the alkali silicate include sodium silicate, potassium silicate, lithium silicate and the like. The water used as the medium of the silica dispersion is not particularly limited as long as it does not inhibit the expression of the desired effect of the present invention. For example, any water such as tap water, distilled water, ion-exchanged water, etc. should be used. Can do.

  The silica sol can be prepared, for example, by the method described in “Inorganic Chemistry Complete Book” (Maruzen, 1986) p292. Various methods for producing a silica sol have been proposed, and a method for neutralizing an alkali silicate, an ion exchange method, a method for hydrolyzing silicon tetrachloride, and the like have been reported. The silica sol of the present invention can be prepared using any of these production methods.

  For example, (a) a silicic acid solution is prepared by bringing a sodium silicate aqueous solution having a concentration of 5 (w / v)% into contact with a hydrogen-type cation exchange resin to dealkalize, and (b) the silicic acid solution. Hydrochloric acid is added to the solution, and the silicate solution is acid-treated at a pH of 2.5 or less and at a temperature of 0 to 90 ° C. (E) Oligosilicate solution was prepared by adding ammonia water to a part of this oligosilicate solution and heating to a temperature of 60-90 ° C. at pH 7-10. Silica sol can be prepared by gradually dropping the remainder of the acid solution. On the other hand, to the oligosilicic acid solution obtained by the steps (a) to (c), (d ′) ammonia water is added to a part thereof, and the mixture is heated to a temperature of 90 to 150 ° C. at pH 7 to 10. However, the silica sol can also be prepared by gradually dropping the remainder of the (e ′) oligosilicic acid solution.

  As the silica sol, a commercially available silica sol (for example, a commercially available water glass) can be used as it is. The silica concentration of the silica sol used in the present invention is preferably 5 to 60% by weight, more preferably 10 to 45% by weight.

  From the viewpoint of imparting the desired chemical structure as described above to the silica component, for example, in the process of preparing a silica dispersion, after obtaining a silica sol, an alkali silicate is added to the sol, It is preferable to adjust the pH of the resulting mixture to a range of 10 to 11.4. From the viewpoint of preventing the gelation of the silica component, it is preferable to adjust the pH range so as not to deviate locally. For example, when adding an alkali silicate, it is added to the silica sol as a mixture with an arbitrary amount of water. It is preferable to do this. The pH can be adjusted by appropriately diluting with water as described above. For example, the pH may be adjusted using an acid containing a group 3B, 4B, or 5B element described above.

  Moreover, as another manufacturing method of the silica dispersion liquid of this invention, the manufacturing method including the process of hydrothermally treating the mixture containing silica sand, water, and an alkali metal containing compound, and melt | dissolving the said silica sand is mentioned. The silica dispersion of the present invention is prepared by, for example, mixing silica sand, an alkali metal-containing compound and water and then dissolving the silica sand by hydrothermal treatment, or after mixing silica sand, an alkali metal-containing compound and water, Anhydrous alkali silicate obtained by hydrothermal treatment and then calcination can be obtained by optionally crushing and then dissolving the silica sand again by hydrothermal treatment. At this time, for example, by adjusting the amounts of water and silica sand, the solid content and the content of the silica component can be made desired.

The SiO ₂ content of the silica sand is preferably 90% by weight or more, more preferably 95% by weight or more, and particularly preferably 97% by weight or more. The shape and average particle diameter of the silica sand are not particularly limited. Examples of the quartz sand include Australian pearl sand and flattery sand, Indonesian sarawak sand, and quartz sand crushed quartz stone.

  Examples of the alkali metal-containing compound include hydroxides, carbonates, nitrates, and sulfates of alkali metal atoms, and sodium is preferable as the alkali metal atom. Preferable examples of the alkali metal-containing compound include sodium hydroxide, sodium carbonate, sodium nitrate, and sodium sulfate.

  Hydrothermal treatment as used herein refers to, for example, an operation of dissolving silica sand under pressure in an alkaline aqueous solution in a nickel crucible, and the pressure condition is preferably 0.5 to 1.8 MPa, more preferably. Is 0.7 to 1.7 MPa, particularly preferably 0.9 to 1.7 MPa. The treatment temperature is preferably 150 to 220 ° C, more preferably 160 to 200 ° C, particularly preferably 170 to 200 ° C, and the treatment time is not particularly limited, but is preferably 1 to 24 hours.

  As a firing method, a known method is usually used, and a method of firing in a range of preferably 300 to 1500 ° C., more preferably 500 to 1300 ° C. is exemplified. The heating time is usually 0.1 to 24 hours. Such firing can usually be performed in a heating furnace such as an electric furnace or a gas furnace.

  After calcination, the obtained anhydrous alkali silicate is pulverized as required and adjusted to a predetermined particle size. For the pulverization, for example, a pulverizer such as a ball mill or a roller mill is used.

  In addition, adjustment of the average particle diameter of solid content particle | grains can be performed by controlling pH and addition density | concentration suitably at the time of aging temperature at the time of silica sol adjustment, aging time control, addition of alkali silicate etc., for example.

  The various other components described above may be appropriately added to and mixed with the silica sol at the same time or after the addition of the alkali silicate or the like to the silica sol, for example.

  The silica dispersion of the present invention can be prepared as described above, and the obtained silica dispersion forms a sol in which solid particles are uniformly dispersed in an aqueous medium.

  The obtained silica dispersion is excellent as a coating material or impregnating material for coating on the surface of various base materials such as inorganic base materials, organic base materials and metal materials, and is applied to the surface of the base material. Used after work. Examples of the inorganic base material include concrete and glass, examples of the organic base material include acrylic resin, urethane resin, epoxy resin, polyester resin, and silicon resin. Examples of the metal material include a plated steel plate. It is done. Of these, particularly suitable for inorganic base materials.

  Coating of the silica dispersion of the present invention on the substrate is selected from known methods such as a brush coating method, a roller method, a spraying method, a spraying method, an impregnation method, and a filling method, and is suitable for the application. Construction is possible by the method. A good coating film (coating film) is formed on the surface of the base material by drying and curing appropriately after the construction. The formation of the coating film is caused by the development of a network structure mainly due to the silica component formed on the surface of the base material and / or with the drying of the silica dispersion partially impregnated in the base material. Formation of the coating film contributes to improvement of durability of the substrate.

  The present invention also provides a coating film obtained by applying the silica dispersion of the present invention on a substrate by any of the above-mentioned construction methods, for example, a brush coating method, followed by drying and curing at room temperature. The coating film is excellent in water resistance, weather resistance and the like, and therefore has excellent durability. By utilizing the high water resistance of the coating film of the present invention, for example, it is possible to prevent sulfation and chlorination of concrete. The coating film is excellent in gas barrier ability. For example, when a coating film is formed on the concrete surface, the effect of preventing the neutralization of the concrete is exhibited. The gas-proofing effect of carbon dioxide etc. is also high, and this property contributes to the prevention of the neutralization of concrete.

  Moreover, the coating film which consists of a silica dispersion liquid of this invention has the water absorption suppression effect of an inorganic porous body. Therefore, this invention also provides the inorganic porous body water absorption inhibitor as one aspect thereof. Inorganic porous materials include concrete, mortar, lightweight aggregates and the like. The said inhibitor consists of the silica dispersion liquid of this invention, and the usage method should just follow the case of a silica dispersion liquid. It is preferable to apply an impregnation method to an aggregate, particularly a recycled aggregate, and the water absorption of the aggregate decreases due to the formation of a coating film. Therefore, the use of the inorganic porous material water absorption inhibitor of the present invention contributes to the improvement of the durability of the aggregate.

  In the following, unless otherwise specified, “part” and “%” are based on weight.

The following commercially available products (manufactured by Nissan Chemical Co., Snowtex series) were used for the preparation of the silica dispersion.
(A) -1 solution: silica sol containing colloidal particles having a primary particle size of 1 to 30 nm (a) -2 solution: silica sol containing colloidal particles having a primary particle size of 30 to 100 nm

  The final silica concentrations of (a) -1 solution and (a) -2 solution were adjusted to 20% by appropriately diluting with ion-exchanged water.

Example 1
After mixing 5 parts of commercially available sodium silicate (No. 3 water glass: silicon compound 30%, sodium compound 10%; manufactured by Osaka Silica Co., Ltd.) and 5 parts of ion-exchanged water, 100 parts of the above (a) -2 solution To prepare a test solution. The solid content of this test solution was 20%, and the silica component content in the solid was 98%. The relative amount of the Q ₂ structure was 1%, the Q ₃ / Q ₄ ratio was 0.47, and the average particle size of the solid content particles was 0.12 μm.

Example 2
After mixing 5 parts of commercially available sodium silicate (No. 3 water glass) and 5 parts of ion-exchanged water, it was added to the mixed solution of the above (a) -1 solution and (a) -2 solution 50 parts and tested. A liquid was prepared. The solid content of this test solution was 20%, and the silica component content in the solid was 98%. The relative amount of the Q ₂ structure was 0%, the Q ₃ / Q ₄ ratio was 0.47, and the average particle size of the solid content particles was 0.11 μm.

Example 3
After mixing 10 parts of commercially available sodium silicate (No. 3 water glass) and 10 parts of ion-exchanged water, it was added to the above mixed solution of 50 parts of (a) -1 and 50 parts of (a) -2 and tested. A liquid was prepared. The solid content of this test solution was 19%, and the silica component content in the solid content was 98%. The relative amount of the Q ₂ structure was 3%, the Q ₃ / Q ₄ ratio was 0.48, and the average particle size of the solid content particles was 0.11 μm.

Example 4
An anionic surfactant sodium lauryl ether sulfate (trade name: EMAL 20C; manufactured by Kao Corporation) was mixed with 100 ppm and 5000 ppm isopropanol, and then added to the silica dispersion described in Example 2 to prepare a test solution. Prepared.

Example 5
After adding 2% of MgO powder to the silica dispersion described in Example 2, it was uniformly dispersed with an ultrasonic disperser to prepare a test solution.

Example 6
After mixing 5 parts of commercially available sodium silicate (No. 3 water glass) and 5 parts of ion exchange water, it was added to 100 parts of the above (a) -1 solution to prepare a test solution. The solid content of this test solution was 20%, and the silica component content in the solid was 98%. The relative amount of the Q ₂ structure was 0%, the Q ₃ / Q ₄ ratio was 0.69, and the average particle size of the solid content particles was 0.26 μm.

Example 7
After mixing 5 parts of commercially available sodium silicate (No. 3 water glass) and 5 parts of ion-exchanged water, it was added to 100 parts of commercially available colloidal silica (trade name: Spherica Slurry 550, manufactured by Catalyst Kasei Kogyo Co., Ltd.) for testing. A liquid was prepared. The solid content of this test solution was 20%, and the silica component content in the solid was 98%. The relative amount of the Q ₂ structure was 0%, the Q ₃ / Q ₄ ratio was 0.15, and the average particle size of the solid content particles was 0.65 μm.

  The pH of the silica dispersions of Examples 1 to 7 was in the range of 10 to 11.4, and uniform dispersions were obtained.

Comparative Example 1
Said (a) -1 liquid was made into the test liquid as it was. The solid content of this test solution was 20%, and the silica component content in the solid content was 99.3%. The pH of the test solution was 9.7.

Comparative Example 2
A test solution was prepared by mixing 50 parts of commercially available sodium silicate (No. 3 water glass) and 50 parts of ion-exchanged water. The solid content of this test solution was 20%, and the silica component content in the solid was 75%. The pH of the test solution was 11.5.

Comparative Example 3
It was prepared under the same conditions as in Example 1 except that 5 parts of sodium silicate was mixed with 100 parts of the above-mentioned (a) -2 solution and then 5 parts of ion-exchanged water was mixed. However, a gel was formed and a uniform dispersion was not obtained, and no subsequent evaluation was performed.

Test Example 1 Coating Film Property Test The coating property (film forming property) of each test solution obtained in Examples 1 to 7 and Comparative Examples 1 and 2 was evaluated. That is, about 0.1 g of the test solution was applied on a glass plate (25 mm × 75 mm) by a brush coating method, and the film formation state after drying was visually observed based on the following evaluation criteria under an optical microscope. To evaluate the coating properties. Table 1 shows the results of the coating property test of each test solution.

〔Evaluation criteria〕
◎: Demonstrate sufficient film formation, no cracks ○: Film formation, but some cracks (5 or more cracks within 1mm width)
△: No film-forming property and crack

Test Example 2 Water Resistance Test The water resistance of the coating film formed using each test solution obtained in Examples 1-7 and Comparative Examples 1-2 was evaluated. That is, about 0.1 g of the test solution was applied onto a glass plate (25 mm × 75 mm) by a brush coating method, and after drying, the obtained film was immersed in water for 24 hours, and the film remaining on the glass plate The amount was evaluated by visual observation based on the following evaluation criteria under observation with an optical microscope, and was evaluated as water resistance. Table 1 shows the results of the water resistance test of the coating film obtained with each test solution.

〔Evaluation criteria〕
A: Almost remaining (80% or more remains)
○: Half or more remaining Δ: Almost dissolved (50% or more dissolved)

  From the results of Table 1, the test solutions obtained in Examples 1 to 7 all showed good coating properties as compared with the test solutions obtained in Comparative Examples 1 and 2, and the coating films were It turns out that it shows the outstanding water resistance. FIG. 1 shows the state of a coating film (50 times magnification) obtained using the test liquid of Example 2 (silica dispersion of the present invention) and the test liquid of Comparative Example 1 (comparative composition), respectively.

Test Example 3 Water Absorption Inhibiting Capacity Test The water absorption inhibiting ability of the coating film formed using each test solution obtained in Examples 1 to 7 and Comparative Examples 1 to 2 was evaluated. In other words, standard sand (Toyoura, Yamaguchi Prefecture) with an average particle size of 0.2mm, ordinary Portland cement and water were blended in a ratio (weight ratio) of 1: 1: 0.3, and a mortar specimen with a diameter of 5cm and a height of 0.5cm was prepared. It was prepared, dipped in each test solution for 5 minutes, then pulled up and dried at room temperature for 24 hours. After drying, the mortar specimen was immersed in ion exchange water for 30 minutes. The rate of weight change of the mortar specimen before and after immersion in ion-exchanged water was determined as the water absorption rate, and the water absorption inhibiting ability was evaluated based on the water absorption rate. The lower the water absorption rate, the better the water absorption suppressing ability. In addition, the water absorption rate was calculated | required before and after immersion in ion-exchange water also about the mortar specimen which is not immersed in a test liquid as a blank. Table 2 shows the results of the water absorption inhibiting ability test of the coating film obtained with each test solution.

  From the results of Table 2, it can be seen that the test liquids obtained in Examples 1 to 7 have excellent water absorption suppression ability as compared with the test liquids obtained in Comparative Examples 1 and 2. . In particular, in the coating film made of the test solution obtained in Example 4, remarkable water absorption suppression ability was recognized.

Example 8
Sodium methyl siliconate (chemical formula: CH ₅ NaO ₃ Si) was used as a compound having a Si—C bond. To 100 parts of the silica dispersion described in Example 2, 3.1 parts of a 30% aqueous solution of sodium methylsiliconate was added and mixed with stirring to prepare a sodium methylsiliconate-containing silica dispersion. The solid content of the silica dispersion was 21%, and the silica component content in the solid was 98%. The relative amount of the Q ₂ structure was 0%, the Q ₃ / Q ₄ ratio was 0.47, and the average particle size of the solid content particles was 0.11 μm. Moreover, in the said silica dispersion liquid, content of Si which forms a Si-C bond was 2.3 mol% in all the Si.

  When the film property test was performed under the same conditions as in Test Example 1, the film formability on the glass plate was good (◎). Further, the contact angle between the dry film on the glass plate obtained under the same conditions as in Test Example 1 and water was measured with a contact angle measuring device (manufactured by Kyowa Interface Science Co., Ltd.). Table 3 shows the change over time in the contact angle between the dry film on the glass plate and water immediately after the formation of the dry film, as compared with the case of the silica dispersion of Example 2.

  Furthermore, about 0.2 g of a silica dispersion was applied to the surface of the mortar specimen prepared in Test Example 3 by a brush coating method, and the contact angle was measured after drying for 1 day. Table 4 shows the results compared with the case of the silica dispersion of Example 2 and the case of no application.

  From the results of Table 3, it can be seen that the water repellency of the dry film is continuously improved by adding sodium methylsiliconate to the silica dispersion. In this test, the persistence of water repellency up to 1 hour was observed, but this water repellency is maintained until the coating disappears. Moreover, it can be seen from the results in Table 4 that the water repellency of the dry film is exhibited even when the dry film is formed on the surface of the mortar specimen. Therefore, for example, by forming a water-repellent film having excellent durability on the concrete surface, the durability of the concrete can be expected to be improved.

  INDUSTRIAL APPLICABILITY According to the present invention, there is provided an aqueous silica dispersion excellent in coating properties and durability of a formed coating film, which is suitably used as a coating material or an impregnation material for coating various substrate surfaces.

FIG. 1 shows the state of a coating film formed on a glass plate obtained using the test liquid of Example 2 (silica dispersion of the present invention) and the test liquid of Comparative Example 1 (comparative composition), respectively. It is the optical micrograph shown (magnification 50 times).

Claims (6)

An inorganic porous body water absorption inhibitor comprising an aqueous silica dispersion having a solid content of 5 to 75% by weight and a silica component content of 97 to 99% by weight in the solid content. In the attribution of the spectrum by ²⁹ Si-NMR of the silica component, the ratio of the area of the signal indicating the Q ₂ structure to the total area of the signal indicating the Q _n (n = 0 to 4) structure is 5% or less, and the Q ₃ structure 2. The inorganic porous body water absorption inhibitor according to claim 1, wherein the ratio of the area of the signal indicating Q ₂ and the area of the signal indicating Q ₄ structure is 0.1 ≦ Q ₃ / Q ₄ ≦ 0.6. The inorganic porous body water absorption inhibitor according to claim 1 or 2, wherein the average particle size of the solid particles is in the range of 0.01 to 0.8 µm. When the silica component contains Si that forms a Si—C bond and / or Si that does not form a Si—C bond, and contains Si that forms a Si—C bond, the Si—C bond The inorganic porous body water-absorption inhibitor according to any one of claims 1 to 3, wherein the content of Si that forms bismuth is 0.01 to 30 mol% in the total Si. The inorganic porous body water absorption inhibitor according to any one of claims 1 to 4, further comprising a surfactant and / or an alcohol . The inorganic porous body water absorption inhibitor according to any one of claims 1 to 5, further comprising ceramic powder and / or a color pigment.

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